Propeller



. Patented May26, 1936 UNITED STATES PATENT oFF- ca 2,041,849 j mornnnnn7 Ernest a. McCauley, mm. Ohio Application July 1, 1932, Serial No.620,462

' 48 Claims. (01. 170 159) This invention relates'to propellers, andmore particularly to aeronautical propellers of the type in which aplurality of blades are connected to a hub portion. A q

It is well known that propellers have been previously constructed ofconventional airfoil sections and of solid metal construction; likewiseattempts have been made to build propellers of stampings of thinsheet.metal. Heretofore in the construction of propellers of thischaracter the blade sections were of such thickness that they did nothave a very high efiiciency above a tip velocity of approximately 950feet per second and at speeds beyond this {range their efficiency felloff considerably due to the lack of sufficient rigidity in thecrosssectional area of the blade sections, whichpermitted the outer endor .tip portion of the blade to violently flutter andeventually'crystallize and break off, due to fatigue of the thinmaterial.

Furthermore, previous attempts toprovlde a metal propeller withsubstantially solid blades have in general resulted in merely decreasingthe cross-sectional area of the blade section a small proportion belowthose used on the conventional wood propellers, and propellersconstructed thusly, while they have shown advantages of from two to fivepercent in efliciency over the wood propellers, have nevertheless hadtheir lim- 0 itations in that they were not highly emcient at theprevailing aeronautical tip speeds and were extremely ineflicient in theranges of tip velocities, at and beyond the speed of sound which isapproximately 1186 feetp'er second.

0 Further disadvantages have been the limita tions on the engine speeds,the increasing of'the engine speeds would causethe tip velocities of thepropellers to be increased beyond their best 'eflicient operating range,and flutter violently,

v0 thereby producing objectionable noises. I

Itis therefore a primary object of this invention' to provide apropeller, of such construction that will'permit an increase in thepresent engine speeds with a consequent increase in the .5 'efflciencyand horsepower of the engines, and that will operate eiiiciently atspeeds in the range at and beyond the speed of sound. Accordingly, Iprovide a propeller of metal so constructed and arranged as to affordvery thin aerodynamically i0 eiiicient blade sections of relativelysmall crosssectional area'in similar proportion to the width andthickness thereohwhich sections vary in width and thickness thruout thelength of the blade and are so designed as to prevent a fluti5 tering ofthe blade, and especially at the outer end or tip portion thereotwhenthe same is rotating at high velocity and to possess an extremely highrigidity to withstand torsional and thrust stresses that are applied tosaid sections.

Furthermore, I provide a propeller of this 5 character with an airfoilof such shape or contour that will improve the aerodynamic proper tiesof the propeller by diminishing the prejudicial deformation due tothrust and torque at high tip velocities that will approach or exceed 10950 feet per second, which would be substantially equivalent in a smallpropeller, to approximately 5 feet diameter running at 3600 R. P. M.,and in a large propeller approximately feet diameter running at 1250 R.P. M., and that will 15 resist during such velocities bending or flexionsuiiiciently to prevent failure of the. section against the ensuingthrust and torque loadings and avoid excessive noises.

A still further object of this invention is ti) provide in a blade ofthis character a distribution of the material in such manner as toprovide a propeller of utmost strength and rigidity to withstand thehigh loadings due to centrifugal force, and the combined bendingstresses of thrust and torque. Another object of my invention is theprovision of a. propeller of this character having a hub portion inabutting engagement. with the blades to provide a solid base on the hubfor clamping the blades, and means detachably connected to said bladesand hub for retaining the blades against the entire action of thecentrifugal force and a major portion of the rotational torque loads,said means permitting of an angular setting of the blades.

'A'still further'object of my invention is to provide a very accurateand simple means 01' balancing the blades. j e

Various other-objects and advantages will ap- 40 pear from an inspectionof the following specifl cation in connection with the drawing which ishereto annexed and forms a part thereof and in i which Fig. 1 is a planview of a propeller constructed in accordance with my invention;

Fig. 2 is a view similar to Fig. 1 showing an enlarged view of thepropeller blade; I

Fig. 3, Fig. 3a, Fig. 312, Fig. 30, Fig. 3d;Fig. 3e,

Fig. 3 .Fig. 39, Fig. 3h, Fig.3i, Fig. 3f, are trans- 0 the bladeshowing the general contour or proflle of the blade airfoil sections;

Fig. 5, Fig. 5a, Fig. 5b, and Fig. 5c, are a fractional outline of ablade tip portion together with corresponding various cross sectionshowing a variation having the various cross sections with the medianline located on line N-N;

Fig. 6, Fig. 6a, Fig. 6b, and Fig. 6c are a view similar to Fig. 5, Fig.5a, Fig. 5b, and Fig. 50 showing a further variation;

Fig. 7 is an enlarged fractional view in longitudinal cross-section ofthe blade showing the root end anda portion of the shank;

Fig. 8 is a front elevational view showing the hub in quarter sectionand fragmentary portions of the blades;

Fig. 9 is a plan view corresponding to Fig. 5 in the position, and

Fig. 10 is an enlarged view of the right of Fig. 8.

Referring to the drawing and with particular reference to Figs. 8 and 9the hub portion iii of the propeller comprises the axle portion i2 andthe integral radially extending socket portions I4 which extend arelatively short distance laterally away from the axle portion.

The hub portion is preferably in the form of a steel drop-forging, theaxle portion having an internal cylindrical spline bore i6 provided withsplines H by means of which the hub is securely mounted on a propellershaft (not shown). The socket portions H are preferably formed withshallow cylindrical bores I that extend inwardly to a surfacecorresponding to the outer wall surface of the axle portion. The ends ofthe socket portions I4 are each formed with outwardly turned flange 20,the outwardly presenting faces 22 of which are disposed in planes atright angles to the longitudinal axis a:-a: of the hub or propeller andthe inwardly presenting faces 24 of which are made frustro-conical for apurpose hereinafter described.

As herein disclosed a novel propeller blade 26 preferably made of metalin the form of a steel forging and in a manner hereinafter described isattached to each of the hub socket portions by providing the root of theblade with a projection 28 that is received within the bore i 8 of thesocket portion and with an outwardly turned annular flange 32 positionedat a relatively short distance from the outer end of the projection 28so as to be capable of having its face 34 about the face 22 of flange 20of the hub, this projection serving, when the blade is connected to thehub, for a purpose hereinafter described.

Each blade is attached as shown in Figs. 8 and 9, to the hub and heldagainst centrifugal forces by means of a split clamp 36 havingsplit-clamp parts 38 and 40, each of which is of substantiallysemi-cylindrical construction having inturned flanges 42 and 44, theformer flange being formed with a straight inner face 46 contacting withthe face 48 on the propeller blade and the latter flange having afrustro-conical face 50 contacting with the face 24 on the hub flange.

' The clamp parts 36 and 40 of each pair of clamps 36, that are disposedon opposite sides of the axle portion of the hub are provided with lugs52 so that the clamp parts may be secured together by means of bolts 54which, when tightened, cause the clamp parts ,to move closer together inthe direction of the longitudinal axis of the propeller and due to thetapered faces or surfaces 24 and 50 the blades are caused to moveslightly inwardly towards the propeller axis of rotation z-z with theflanges of the blade held in tight abutting engagement with the flangesof the hub so that the blades are held rigidly against a solid base onthe hub. The clamp parts 36 and 40 of each clamp form practically thesole restraining means for holding the blades against centrifugal forceand serve to take substantially the entire load in the transmission ofrotational torque force to the blades.

Each of the blades, as shown consists of a cylindrical root portion 56,as shown in Fig. 2 and Fig. 3, a shank portion 56, comprising Fig. 3aand Fig. 31) having the leading and trailing edges 4 and 5 respectively,and an upper surface 9 and a lower surface 6 as illustrated, and anairfoil portion 30, with cross sections as shown in Fig. 30, Fig. 3d,Fig. 3e, Fig. 31, Fig. 3a, Fig. 3h, Fig. 3i, Fig. 37', having theleading and trailing edges 2 and 3 respectively, and upper surface 60and lower surface 62, as also shown in Fig. 4, which planfonn profile inFig. 2 between the sections of Fig. 30 to Fig. 37' provide a contour ofthe leading and trailing edges of opposite convex curved profiles, thathas the maximum width at a point substantially midway of the bladelength, from the axis of rotation, and is preferably in the form of asteel forging which may be heat-treated to a high tensile strength, andis formed with relatively thin sections in which the material is sodistributed as to present the ut-' most strength 'and rigidity to theforces of centrifugal, thrust and torque. With the use of special alloysteel, such as nickel-chrome molybdenum or its equivalent, heat treatedto a tensile strength of approximately from 150,000 to 175,000 lbs. persquare inch, it will be apparent that thinner blade sections may beemployed than is possible to obtain with other materials of less tensilestrength provided, however, a proper distribution of the material ismade without sacrifice in the efficiency of the blade section rangingsubstantially in diameters from 5 feet to 15 feet or greater.

In accordance with my invention, therefore, in order to provide anairfoil section of such contour and thinness that greater efllciency maybe obtained without substantially increasing the weight of the blade, asa whole, when compared with other blades of the same diameter nowgenerally in use and made in the form of solid aluminum alloy or steelforgings, I have designed an airfoil section, as shown in Fig. 4, havinga profile such that the upper surface 60 thereof is convexly arcuate andthe lower surface 62 is in the form of an ogee or reverse curve, bothsurfaces merging into somewhat sharply rounded edges 2 and 3 and soarranged that the swelling or thicker portion is disposed adjacent theleading edge 2 and the arched or thin portion adjacent the trailing edge3. There is thus provided a blade in which the leading edge portion isformed with a double-convex surface and the trailing edge portion with aconcavo-convex surface, the point of 'tangency or merging of the convexand concave portions 68 and 10 of the lower surface 62 occurring approximately one third the chord length of the airfoil section from itsleading edge 2 as represented by the line Y-Y on Fig. 2.

The double convex or leading edge portion 12 has each cross sectionrelatively gradually increasing in thickness from the tip end of theblade to the inner end of the shank portion to into the cylindricalsection it at the root 'end' relatively gradually increasing in"thickness throughout the length of the airfoil-portion '30 of the blade,and in a corresponding manner, so that the trailing edge portionbecauseof its peculiar arched construction which maybe formed by.forging in suitable dies, that will not only have a high strength weightratiobut will also possess suflicient rigidity and stiffness towithstand bending and deflection from the thrust loadings and willfurthermore supplement the leading edge portion 12 to providesufiicie'nt strength to withstand the forces of torque load-g ings.

According to; these improvements thegreater mass of the material will belocated near the leading edge and the center of gravities 16 both inplan and elevation of the blade sections from tip, to root are disposedin a straight line that is coincident with the longitudinal axes x--xand E-E respectively, of the blade or propeller. This may be changedso that the median line of grave will follow closelyjalong the path ofthe line 25 i -Y on the leading edge portion i2, and may even crossoverthe axis X-X near the outer' extremity of the blade to the trailing edgeportion it. The centrifugal force will thus assist in-keeping the bladeas a whole from deflecting rearwardin the path of rotation and addfurther strength to'theblade in this direction.

The shank portion '58 of the blade has its cross sections graduallyvarying from a circular sec- .tion it at its inner end to an airfoilsection W at its inner end that consists of Fig. 3, Fig. 3a,

and Fig. 3b, which planform in Fig; 2 provides a contour of the leadingedge i and trailing edge 5 of opposite concave curved profiles thatmerge portion of the blade, and. is formed with a longitudinallydisposed conical bore tithe base of which is disposed at the root end ofthe blade. The dimensions of this cone are such that the walls of theshank portion are of sumcient thickness as to provide the requiredstrength'to sustain the operative stresses of the propeller and eachcross section thereof has its material increasing in area incontinuation of'the gradual increase in the cross sections of theairfoil portion it to provide ablade whose cross-sectional areasgradually increase from tip to root. With that a highlyrigid and emcientblade is obtained. V

The cylindrical projection or extention M of the blade root is made tohave a close turning fit with its complementary socket or bore it so asto center the blade and readily permit an adjustment thereof to vary thepitch angle and, also, provides a bearing area which together with thebearing area afforded by the abutting faces 22 and 3d of the fiangestiland 32 respectively resists deflection in any direction of the blade atthe point of engagement with thehub.

By reason of its construction mypropeller is the proper balance.

capable of being horizontally'balanced without adding weight as has beenthe practice heretofore. It is, of course, well known that afterassemblingthe blades complete with the hub a balance must be obtainedand in accordance with my invention this may be. obtained by facing offthe necessary amount of material of the abutting face 34 of the flange32 of that blade which is heavy in balance thus allowing the weight ofthe entire blade to be moved inwardly towards the axis ZZ of rotation ofthe hub when assembly is again made to thereby obtain In Fig. 5, Fig.5a, Fig. 5b, and Fig. 50, I have shown a propeller blade constructed ina man-' ner as hereinabove described except that the tip end portionisprovided with a substantially flat bottom face or under surface 86 whichgradually merges longitudinally into the ogee or reverse curve of thelower surface 62 of the adjoining airfoil portion, and having theleading and trailing edges 6 and 1 respectively, merging with 2 and 3 ata. point substantially as shown in Fig. 5a. the equivalent to Fig. 3%. r

A further variation of propeller construction embraced in my inventionis shown in Fig. '6, Fig. 6a, Fig. '61), and Fig. 6c. The propellerblade of this propeller is similar to thatdescribed in connection withFig. 3 to Fig. 37', except that the center of gravities of theblade'sections which lie on the neutral line N--N, are inclineddownwardly and outwardly with respect to the longitudinal axisE-E asviewed in Fig. 6 or in the direction of thrust or forward movement ofthe propeller, starting from a point about one fourth the length of theblade measured from the root end-and terminating at the tip end thereof.

' It will thus be seen that with this construction the centrifugal forcewill provide a restoring force tending to'position the center of gravityline N-N in coincidence with the longitudinal axis E-E of the propellerand will thereby prevent the bending of the blade, especially at the tipend, by the thrust loads exerted thereon.

. While the foregoing description defines a blade made of solid steelconstruction, it is intended that the scope of this invention pertainingto the characteristics of the airfoil section may be applied to bladesof other suitable materials, and other variations from the airfoildescribed and the method to provide rigidity in a thin section may bemade by those skilled in the art, without departing from the spirit ofthe invention. Reference will therefore be had to the appended claimsfor a definition of the limits of the invention.

What I claim and desire to secure by Letters Patent is: Y

1. A propeller blade'having an outer portion of airfoil cross-section ofthe character described, said outer portion gradually increasing incross- ,sectional area from the tip inward, a cylindrical root portionadapted for anchorage to a propeller hub and a. shank portion exteriorof said hub connection of cross-section gradually varying from acylindrical to theouter portion airfoil section, saidblade having alongitudinally disposed conical bore extending thruout the length of theroot portion and into the shank portion,

said conical bore being of such diameter and depth as to provide agradually increasing crosssectional area of the blade from the tiptowards the root andsubstantially thruout the entire length of theblade.

, ly the entire length of the root and shank portions.

3. A propeller blade having an outer portion of solid airfoilcross-section of the character described, said outer portion graduallyincreasing in cross-sectional area from the tip inward, a cylindricalroot portion adapted for anchorage to a propeller hub and a shankportion exterior of said hub connection of cross-section graduallyvarying from a cylindrical to the outer portion airfoil section, saidblade having a central longitudinal tapering bore of circularcrosssection formed within the root and shank portions, said boretapering inwardly from the root of the blade and in such manner as toprovide a gradually increasing cross-sectional area from the tip towardsthe root and substantially thruout the entire length of the blade.

4. A propeller blade having an outer. portion'of airfoil cross-sectionof the character described, said outer portion gradually varyingincross-sectional area, a cylindrical root portion adapted for anchorageto a propeller hub and a shank portion exterior of said hub connectionof cross-sec-' tion gradually varying from a cylindrical to said airfoilsection and said blade having the leading edge portion that extendsforward approximately from the longitudinal axisof the blade of suchvarying cross-sectional area throughout the length as to provide atapering beam portion along the leading edge of sufficient strength tosustain a major portion of the torque stress-in service operation of theblade.

5. A propeller blade in which the airfoil crosssections are formed withconcavo-convex lower surfaces and convex upper surfaces having similarproportions in'width and thickness and'in which the material is sodistributed as to locate the median line of gravity in substantialcoincidence with the blade axes in both longitudinal planes thereof.

6. A propeller blade in which the airfoil crosssections are formed withconcavo-convex trailing edge portions disposed rearward of thelongitudinal axis of the blade and reduced in mass sufficiently tolocate the median line of gravity in substantial coincidence with theblade axes in both longitudinal planes thereof, so that the trailingedge portion of arched construction forms a high strength weight ratioto provide sufllcient strength to withstand deflection from thrustloadings.

7. A propeller blade in which the airfoil crosssections are formed withconcavo-convex trailing edge portions disposed rearward of thelongitudinal axis of the blade and reduced in mass sufliciently tolocate the median line of gravity in substantial coincidence with theblade axis in the planform plane, and forward with respect to the thrustside of the blade, in the plane of rotation, said trailing edge portionof arched construction in connection with the restoring action ofcentrifugal force will provide utmost rigidity to withstand deflectionfrom thrust loadings.

8. A propeller blade havingits median line of gravity for substantiallythe blade length disposed at substantially one-third the length of theblade sections measured from the leading edge and having that portionbetween the median line and leading edge'conflned with in convexlycurved upper and lower surfaces and constituting a tapering beam,extending along the leading edge throughout the length of the blade fromroot to tip, to sustain a major portion of the torque stress' in theblade.

. 9. A propeller blade having the median line of gravity forsubstantially the blade length disposed at substantially one-third thelength of the blade sections measured from the leading edge and havingthat portion between the median line and leading edge confined withinconvexly curved upper and lower surfaces throughout the length of theblade, and constituting a virtual tapering beam, the relative thicknessof the cross-sections of said beam increasing gradually from the tip tothe root end of the blade.

10. A propeller blade having a'hollow shank inner portion and anouterportion having the and lower surfaces and the trailing portion formedwith concavo convex surfaces that mergerespectively with said upper andlower leading edge surfaces, the sections of said. blade diminishing inarea from the root to the tip at a progressively decreasing rate,whereby the ratio of thickness vto thevchord of the cross-sections willprovideutmost rigidity andstrengt'h to the blade.

12, A propeller comprising a hub having blade mounting members, bladeshaving their inner ends mounted against and within said members andmeans for clamping the inner ends of said mounting members, bladeshaving their inner ends mounted against and within said members andmeans for clamping the inner ends of said blades to the members of saidhub in such a man'- ner that the driving force of said hub istransmitted thru said means to said blades, said blades and membershaving telescoping parts for locating said blades within said hub, saidmeans for clamping the ends of said blades with the hub members forattaching the bladesto the hubs in such manner that the driving force ofsaid hub is transmitted thru said means to said blades.

14. A propeller comprising a hub having sockets provided with flanges,bladeshaving their inner ends formed with flanges and projections forabutting with the flanges of said hub and said projections are receivedwithin said sockets for centralizing said blades, and means forattaching the blades to the hub in such manner that substantially allthe driving stresses of hub operation are transmitted thru said flangesto the blades.

15. A propeller comprising a hub having a plurality of flanges andsockets to abut against similar flanges on the root end of the bladesprovided with projections to be mounted in said sockets,

said sockets to provide-a driving means from said hub to said blades andmeans for retaining said blades with said hub.

16. An airplane propeller comprising a pluralityoi' blades havingcylindrical flanges and pro- Jections at their inner ends, a hubhavingsockets and cylindrical base flanges inter-fitting and in abuttingengagement with said projections and flanges of said blades, and meansfor attaching said blades to said hub for rigidly securing the blades tothe hub in such manner that the centrifugal force of said blades istransmitted through said means to said hub, and the, rotational torqueforce'is transmitted through the abutting of said flanges on the hub'andblades.

17. A propeller blade of solid steel having an airfoil section of thecharacter described, with theleading edge portion having suflicient massto improve the aerodynamic properties of the propeller by diminishingthe prejudicial deformation due to thrust and torque stresses exerted onthe blade, said airfoil so constructed and arranged to resist bending orfiexion of the blade from the ensuing thrust and torque loadings.

18. A propeller blade of solid steel having an airfoil section of thecharacter described with the leading edge portion having suflicient massto provide rigidity from the root portionof the blade to-the tip portionto improve the aerodynamic properties of the propeller by diminishingthe" edge portion is of such proportion for utmost a strength andrigidity to withstand the combined loading of centrifugal force andthrust force to prevent excessive flutter of the blade and provide asilent propeller.

2d. A propeller blade of solid steel having an airfoil section of thecharacter described, so constructed and arranged that a distribution ofthe material throughout the blade length along the leading edge portion,and .by arching the trailing edge portion is-of such proportion forutmost strength and rigidity from the root portion of throughout'thelength of the blade substantially from the root portion to the tip, soconstructed- 5 and arrangedthat the leadingedge portionis,

formed with a double convex surfaces, and thetrailing edge portion isformed with a concavoconvex surfaces, the point of tangency of the con-"vex and concave portions on the lowerv surface of the airfoil occurringapproximately one-third of the chord length of the airfoil section fromthe leading edge, said portion of. the blade sections confinedwithin'the double convexsurfaceswhose width and thicknessgraduallydecreases'from root to tip comprises a tapering beam; along theentire leading edge portion of the. blade to add rigidity againstrearward deflection of the blade in the path of rotation against theforces of torque.

T tions confined withinthe concavo-convex surfaces and approximatelytwo-thirds of the chord length of the sections comprises an archedconstruction of varying width and thickness along the trailing edgesections of the blade,.to provide rigidity against forward deflection ofthe blade in the path of rotation against the forces of thrust.

24. A propeller blade having an airfoil section I throughout the lengthof the blade substantially from the root portionto the tip, soconstructed and arranged that the leading edge portion is formed with adouble convex surface, and the trailing edge portion is formed with aconcavoconvex surface, the point of 'tangency of the com --vex andconcave portions on the-lower surface of the airfoil occurringapproximately one-third of the chord length of the airfoil section fromthe leading edge, said sections gradually decreasingin area from theroot portion to the tip of the blade for the purpose described.

25. In a propeller blade, a planformprofile, of such a character thatthe contour of the leading edge and the trailing edge of the outerportion of the blade from the tip inward are formed of convex curvedprofiles, and merge into concave ,curved profiles at the inner shankportion, and

- of such'a character that the contour of the leading edge and thetrailing edge of the outer portion of the blade from the tip inward areformed by convex curved profiles, and merge into concave curved profilesat the inner shank portion, and terminate into a cylindrical profile attheroot end portion of the blade, said planform profile having themaximum width of the blade at a point substantially midway from the axisof ro tation.

27. In a propeller blade,'-an airfoil of the character describedcomprising .concavo-convex surfaces, a planform. profile, of such a.character thatthe contour of the leading edge, and-the trailing edge ofthe outer portion of the blade'from the tip inward are formed by convexcurved profiles, and merge into concave curved profiles at the innershank portion, and terminate into a cylindrical profile at the root endportion of the blade.

28. In a propeller blade of solid steel, having a shank portion at theinner end, and an airfoil portion extending therefrom, said airfoilportion having a concave-convex lower surface of relative similarproportions throughout the length thereof.

29. In a propeller blade of solid steel, having an end projection, acylindrical flanged root end adjoining said projection, a shank portionadjoining said root end, and an airfofl portion adjoining said shankportion, said-airfoil portion having a concavo-convex lower surface ofrelativesimilar proportions throughout the length thereof.

30. In a propeller blade, a planform profile, of such a character thatthe contour of the leading edge and the trailing'edge of the outerportion of the blade from the tip inward are formed of convex curvedprofiles, and merge into concave curved profiles at the inner shankportion, and

terminate into a cylindrical flanged profile at the root end portion ofthe blade provided with a cylindrical projection at the innermost, endof the blade.

31. In a propeller blade, a planform profile, of such a character thatthe contour of the leading edge and the trailing edge of the outerportion of the blade from the tip inward are formed of convex curvedprofiles, and merge into concave curved profiles at the inner shankportion, and terminate into a cylindrical fianged profile at the rootend portion, and a cylindrical projection adjoining the flanged profileat the innermost. end of the blade.

32. In a propeller blade, a planform profile, of such a character thatthe contour of the leading edge and the trailing edge of the outerportion of the blade from the 'tip inward are formed by convex curvedprofiles, and merge intoconcave curved profiles at the shank portion,and terminate into,

a cylindrical profile at the root end portion of the blade, saidplanform profile having the maximum width of the blade at a pointintermediate the tip and root end portion.

33. In a propeller blade, having a shank portion at the inner end, andan airfoil portion extending therefrom, said airfoil portion having aconcave-convex lower surface for a greater portion of the blade length,and merging into a relatively fiat lower surface substantiallythroughout the outer extremity of the blade.

34. In a propeller blade, having a hollow shank I portion at the innerend, and an airfoil portion extending therefrom,'said airfoil portionhaving a concavo-convex lower surface for a greater portion of the bladelength, and merging into a relatively fiat lower surface substantiallythroughout the outer extremity of the blade.

35. In a propeller blade, having a cylindrical 'lower surface throughoutthe outer extremity of the blade.

3'7. In a propeller blade, having a cylindrical flanged root end andprojection, a shank portion adjoining said root end, and an airfoilportion extending therefrom, said airfoil portion having. a

concave-convex lower surface fora greater length of the blade, andmerging into a relatively fiat lower surface throughout the outerextremity of the blade.

- 38. A propeller blade having two opposite faces, one face having aconvex surface for the entire length of the blade, the other face havinga concavo-convex surface for a substantial portion of the length of theblade and having a relatively fiat surface for. the portion adjacent theextremity of said blade.

39. A propeller blade having two opposite faces, one face having aconvex surface for the entire length of the blade, the other face havinga concave-convex surface for a substantial portion of the length of theblade and having a relatively fiatsurface for that portion of its lengthwhere the air velocity traversing said surface will approach or exceed,in normal operation, the velocity of 950 feet per second.

40. In a propeller blade having a hollow root and shank formation and anairfoil portion-with surfaces of the character described, said outerportion gradually increasing in area from the tip inward to the rootend, the thrust surface having both concave and convex portions merginginto each other.

41. In an aircraft propeller bladev detachable from a driving hub,having a hollow root portion and a solid airfoil portion extendingtherefrom,

said airfoil portion increasing in area from the tip inward to the rootportion with the thrust surface part concave and part convex eachmerging into the other in varying proportions.

42. In a solid metal propeller blade having an airfoil portion with thinairfoil sections gradually increasing in thickness throughout the lengthof said airfoil portion of the blade, which are formed by arching toprovide a high strength-weight ratio in the airfoil portion of theblade. 7

43. In a solid metal propeller blade having an airfoil portion with thinairfoil sections gradually increasing in thickness throughout the lengthof said airfoil portion of the blade, which are formed byarching of saidairfoil sections to provide a high strength-weight ratio of suificientrigidity and stiffness to withstand deflection against the stressesimposed in service operation of the blade.

44. In a solid metal propeller blade having an airfoil portion for thegreater length of the blade, 'said airfoil portion so constructed andarranged that rigidity is built into a portion of the airfoil portion byarching the section to withstand deflection against the thrust forces inservice operation of the blade;

45. In a solid metal propeller blade having an airfoil portion for thegreater length of the blade, said airfoil portion so constructed andarranged that rigidity is built into one of the surfaces of the airfoilportion by arching the section to. withstand defiection against thethrust and torque forces in service operation of the blade.

46. A propeller having a hub provided with a plurality of solid basesand a cylindrical socket within said bases, blades having flanges andprojections inter-fitting and in abutting engagement with said bases andsockets, and means for attaching said blades to said hub to rigidly holdsaid blades.

4'7. A propeller blade having a rounded leading edge with a radius whosecurvature gradually increases from the tip to the'root portion of theblade, and a leading edge portion confined within oppositely curvedconvexed upper and lower surfaces and merging with said rounded leading76 10 flanged root portion, a shank portion,'and an outer portion ofairfoil section, said outer portion having rounded leading and trailingedges, with a leading edge portion confined within oppositely curvedconvexed upper and lower surfaces, and a trailing edge portionhaving-convexed upper and concaved lower surfaces that merge with theupper and lower convex surfaces of the leading edge portion respectivelyat a point substantially onethird the chord of the blade.

ERNEST G. mum. 1

